1. Field of Invention
This invention relates to a spray tip for airless spraying and, in particular, to an improved mounting of an orifice tip in a spray tip head.
2. Brief Statement of the Prior Art
The field of airless spraying and equipment used has been well established over many decades of use. Typically, paints, stains, lacquers, etc., are sprayed at high pressures, usually from 2,000 to 5,000 psi, through a minute orifice having a shape and configuration which imparts a desired spray pattern to the discharge. Because of the abrasive nature of the liquid and the relatively high pressures employed, parts which are subjected to highly abrasive conditions, such as the orifice tip member, are formed of very high wear-resistant material, e.g., tungsten carbide and the like.
The small diameter orifice of the orifice tip member unavoidably clogs during painting and a universal design has been to mount the carbide tip member in a holder which can be rotated to reverse the carbide tip member between spraying and cleaning positions. In this manner, any clogs in the orifice can be blown out with the high pressure liquid supplied to the spray head.
Because the liquid will discharge as a jet under relatively high pressures when blowing clogs out of the orifice, safety concerns have resulted in the design of spray tip heads with spray guards to prevent placing one's finger adjacent the orifice tip. Another innovation which has been used commercially comprises stepping the diameter of the passageway communicating with the orifice tip member to provide a small diameter orifice in the cleaning position. It has been found that this disrupts the liquid stream and causes atomization and dispersion of the liquid. Other techniques which have been used for a similar result include positioning a diffuser pin (see U.S. Pat. No. 4,508,268) or other obstruction to break up a coherent liquid jet and cause the liquid to atomize into a safe, dispersed spray.
A difficulty with the aforementioned techniques is that they create an undesirable frictional pressure loss that decreases the efficiency of the spraying operation. Also some leakage occurs during cleaning operations as the rotatable member has a reduced sealing surface when it is in the cleaning position. As a consequence, most of the spray tip heads will leak or dribble paint when operated in the cleaning position. This is an inconvenience and annoyance to the spray operator.
Another trend in the airless spray industry is to provide rotatable orifice tip holders which can be operated with finger or hand pressure without the use of wrenches or other tools. This tendency has exacerbated the aforementioned sealing problems as leaks cannot be avoided by increasing the compressive pressure on the seals as such increased pressure would seize the holder and prevent its facile rotation.